Recently, as a drive source for driving a vehicle, a hybrid vehicle which uses both engine and motor has become rapidly popularized and various types of the drive source for such hybrid vehicle became commercially viable. As for a motor for such system, a three-phase synchronous motor has been frequently used. While a hybrid vehicle is normally running, drive side wheels of the vehicle are driven by supplied electricity from an on-board battery and when the vehicle is stopped (under braking operation), the battery is charged by using regeneration of electricity. Thus, now it is common that a reciprocal electricity conversion is performed by providing a capacitor and the inverter device arranged in parallel between the motor and the on-board battery. The number of components for a hybrid vehicle becomes usually increased due to use of a plurality of drive sources for running the vehicle. This may lead to a space problem in which more components than a regular gasoline powered vehicle have to be accommodated in a limited space in the vehicle. Therefore, a strong desire is raised to minimize the size and weight of the capacitor and the inverter device as much as possible.
The inverter device performs frequently current open/close operation using for example, a PWM control (Pulse Width Modulation control). During such PWM control operation, a surge voltage which includes a high frequency component with a large part is generated and such surge voltage is transferred as a switching noise and further, radiated as a radio wave noise. A size or a level of such surge voltage, switching noise or the radio noise varies depending on the structure of the composing electric circuit. For example, when an inductance component “L” is included in the electric circuit, the surge voltage generated upon interruption of certain electric current “I” can be obtained by the formula “V=L·(di/dt)”. This means the value “V” of the surge voltage is proportional to the magnitude of the inductance component “L”. Further, when the circuit components, such as positive and negative electrodes or the conductive members are not symmetrically arranged in a DC electric circuit, a common mode noise may be generated due to a difference in floating inductance and floating electrostatic capacitance. In a three-phase AC electric circuit, if the structure is not symmetrical, impedance non-equilibrium property may be generated which may lead to a cause of noise generation. When a noise is generated, neighboring electronic control devices or various sensors may be ill-affected.
As a countermeasure for solving the problems of surge voltage and switching noises, a snubber circuit is additionally provided to suppress the generation of the surge voltage or an anti-pressure grade of the power semiconductor module of the inverter device is up-graded to increase the tolerance against the surge voltage or the level of carrier frequency wave of the PWM control may be restricted to a smaller value to restrict a steep voltage change. These measures have not sufficiently solved the problems. Adding a snubber circuit increases the manufacturing cost and up-grading the anti-pressure grade increases the ON-resistance of the module which may lead to a reduction of efficiency in operation. Further, when the carrier frequency is limited to a smaller value, the responsibility of the motor control drops. Thus these conventional means have shown non-preferable big side-effects.
As another measure to suppress or prevent the generation of surge voltage, the inventor of the application has proposed an inverter device which has high equilibrium property, three phase type in a patent literature 1 (PL 1). The inverter device of the PL 1 forms a power semiconductor module by connecting a plurality of equilateral triangle shaped power semiconductor chips and shows an arrangement of six power semiconductor modules in regular hexagon shape. In other words, the inverter device according to the patent literature PL 1 has improved the three phase equilibrium property by arranging the three phases symmetrically in a rotation direction, whereas conventional inverter device has the arrangement of the three phases such that both upper and lower arms are arranged in three straight lines, respectively which may lead to generation of non-equilibrium property.
Further, according to a patent literature 2 (PL 2), the inverter device includes a laminate structure in which a positive electrode side conductor, insulated sheet and a negative electrode side conductor are laminated and the inverter device secures creeping distance and space distance necessary for insulation by using an insulator cap. Thus, according to the PL 2, the opposing currents flowing through the positive and negative electrode side conductors can be approximated to improve the inductance reduction effects greatly. The inventor of this PL 2 says that this may eliminate the use of fuse and snubber circuit.
On the other hand, the motor driving control portion is normally connected the capacitor in parallel with the inverter device. It is important for the capacitor to highly densify the electrostatic capacitance portion and to properly select shape depending on the particular use in order to minimize the size and reduce the weight. It is important for a reduction of generation of surge voltage to reduce the inductance component “L”. The patent literatures PL3 and P4 disclose the technology to improve the reduction of inductance in the capacitor.
The patent literature PL3 discloses a capacitor in a case. The two connecting terminals of the capacitor element are penetrating the same side wall of the case and extending out of the case. This can shorten the lead distance of the connecting terminals thereby to reduce inductance (“L” component) of the capacitor compared to the hitherto technology. Further, the patent literature PL4 discloses the metal film capacitor and the electrode structure of the neighboring capacitor elements are arranged in opposite directions with each other and current flows in reverse direction to reduce the internal inductance. The patent literature PL4 further discloses the overlapping arrangement of the first and the second electrode plates (members for wiring) connected to the two sets of capacitor elements. This can also reduce the wiring inductance.